I've removed the evaporator core from a 2000 Discovery, hopefully yours is the same. First remove the kick panel from in front of the passengers seat. Screws hidden in the carpet. Then remove the screws that hold the top half of the case to the lower half and the screws that surround the lower half of the case. If no R134A refrigerant is in the system, remove the two line fittings on the outside, close to the heater hoses. Unplug necessary wires on the inside and slide the lower half of the case out.
Denso service manual.
HVAC Systems | DENSO Heavy Duty
Goto down loads, service manual. See page 40 for a pic of the whole case.
Richard